Lead alloy



May 9, 1944. G. J. DEUSTACHIO LEAD ALLOY Filed March 29, 1941 2 Sheets-Sheet l y 44- G. J. DEUSTACHIO 2,348,333

LEAD ALLOY Filed March 29. 1941 2 Sheets-Sheet 2 INVENTOR Patented May 9, 1944 UNITED STATES PATENT OFFICE,

LEAD ALLOY Gabriel Joseph DEustachio, Perth Amboy, N. J., assignor to General Cable Corporation, New York, N. Y., a corporation of New Jersey Application March 29, 1941, Serial No. 385,884

8 Claims. (01. 75-166) This invention relates to extruded metal cable sheaths and to lead base alloys suitable therefor, and has for an object the provision of an improved alloy for this purpose.

When subjected to stresses, lead has a tendency to deform slowly or to creep." Even stresses which are only a fraction of those required to develop the short-time breaking strength will cause creep when applied for long periods of time. As examples of stresses which may cause creep in the lead sheath of cables, there may be mentioned the fairly constant internal pressures of oil-filled cables and the varying pressures of solid type cables caused by the combination of hydraulic head and volume change due to temperature cycles. to fatigue under cyclic stresses.

It has long been known that the inclusion of some other metal with lead may produce an alloy of greater strength than lead alone and that extruded sheaths of some of these alloys have greater fatigue resistance and less tendency to creep than sheaths of lead alone. For example, lead may be alloyed with copper'and the resulting material used as a cable sheath. The amount of copper so used is usually 0.06%, or less, since a larger amount of copper than this cannot remain in solution in lead when the alloy is cooled to the freezing point. A sheath made of such an alloy is much superior to a sheath composed of pure lead, both in respect to fatigue resistance and to flow or creep.

When this alloy cools to room temperature, only about 0.02% copper remains in solution in lead, the remaining approximately 0.04% being segregated in the mixture. Certain difiiculties are encountered in the use of this binary leadcopper alloy, especially for cable sheaths, which, in some instances, more than offset its beneficial properties. The undesirable properties result from the uneven segregation, aggregation or concentration of copper particles in certain portions of the mass, these portions being at or near the welds, tongues and flow lines in the finished sheath. The presence of the excess amount of copper in these regions results in an embrittlement and weakness in the finished sheath.

Even with pure or common lead, which is a commercial lead of high purity, these welds, tongues and fiow lines are regions of weakness unless refined methods of lead press operation are used to overcome the diificulties encountered with older practices. The use of the vacuum lead press process is one method of reducing or eliminating these difiiculties with common lead. ll According to the present invention, the diillc Lead sheaths are also subject section.

However, in the case of copper-bearing lead,'even sheaths extruded on the vacuum press havefto a degree, this weakness at welds, tongues and flow lines resulting from the segregation of the copper content and its aggregation or concentration at these points.

This uneven distribution of the copper content is most clearly shown by special etching methods which do not dissolve the copper particles but change them to copper oxide which appears as a black deposit. Sections of the binary leadcopper alloy which have been etched according to this procedure show a heavy black deposit of copper oxide in the region of the welds, tongues and fiow lines. This characteristic of the etched surface has not commonly been observed because the etching methods which are in most general use either remove the copper from the etched surface or do not leave it'in the readily visible form resulting from this etching procedure.

A slight variation of the etching procedure, designed to bring out the grain structure in the same sections, reveals groups of grains of much smaller size than in the major portion of the cross The disadvantage to practical service due to the weakness produced by this uneven segregation, aggregation or concentration of copper in the regions of the welds, tongues and fiow lines is shown by the results of an extensive series of tests in which cable sheaths of various types were subjected to internal hydrostatic pressure.

Tests in one series, extending over a period of a few days, which may be referred to as shortterm tests, were performed on tightly sealed cables in which electric current was circulated in the conductors to heat them. This resulted in heating and expansion of the saturant and, in turn, in increased pressure on the sheath. The rate of heating was so controlled that the internal hydrostatic pressure as measured by a gauge did not exceed 100 to 125 lbs. per sq. in., corresponding to a fiber stress in the sheath of about 1000 to 1200 lbs. per sq. in. As the sheath stretched, the current was increased but limited to a vain producing a conductor temperature of 95 (3., th corresponding sheath temperature being to C. In the case of sheaths formed of commo lead, the sheath stretched sumciently to take car of the expansion and no rupture resulted; bu in the case of lead-copper sheaths, rupture di occur in a large proportion of specimens, th rupture taking the form of longitudinal slit along the weld regions.

ties encountered with these binary alloys of lead and copper are overcome by the inclusion of a third metal which is mutually soluble with either of the first two metals. For example, tin may be used because it satisfies these conditions and produces excellent results.

Tin has been found to produce good results when added in amounts of from 0,03% to 0.5%. Most of the benefits are obtained with amounts of from 0.06% to 0.12%. Ordinarily, because no further pronounced benefits are obtained and because of the increase incost, amounts greater than 0.12% are not used. If amounts in excess of 0.5% are used, this results in gradually reducd creep strength, though up to 3% is not particularly harmful. In the other direction, definite benefits are found with amounts as low as 0.03%, and some benefits with even less.

As an example, fora lead base copper alloy containing 0.06% copper, good results were obtained with a tin content of 0.06% to 0.12%, as shown by test data hereinbelow.

, Where the binary lead-copper alloy is used, it

is the common practice to use the full 0.06% copper which is retained in solution at the melting point of the alloy, because the beneficial efiect of the copper addition falls off rapidly with smaller amounts. However, when tin is included in a ternary alloy of lead-copper-tin, the effects of the tin are such that a useful product will result, even where copper is present in amounts less than 0.06%, say 0.03%, simply retaining whatever valuable properties may be imparted by such amounts of copper as are used. n the other hand, the use of tin makes it practical to use more than 0.06% copper, up to 0.08% copper having been found permissible. For any amount of copper within this range, the amount of tin to be used falls within the same range as for 0.06%

copper.

Tests and observations have shown that concentration of copper along tongues, flow lines and welds which characterizes th binary alloy is substantially absent in the ternary alloy of the present invention. This may be seen in the accompanying drawings, wherein:

Fig. 1 is a photomicrograph at l2 diameter magnification of one of the weld regions of a cable sheath formed of a binary alloy containing 0.06% copper and the balance lead. The sample was etched for detection of copper segregation. The black regions represent the excess copper and l l indicates the weld.

Fig. 2 is a photomicrograph at the same magnification and of the same binary alloy etched in the same way as in Fig. 1, but taken in the region of the tongues and flow lines. The black regions at the boundaries of the tongues where copper aggregation occurs is indicated by the numeral l2.

Fig. 3 is a photomicrograph at the same magniiication and of the same binary alloy as in Fig. 1, but etched and treated to bring out the grain structure in the tongue region, such as that shown in Fig. 2. During etching, the specimen was swabbed to remove the copper oxide and consequently the black areas are absent. The microstructure reveals a concentration of very minute grains at the boundaries of the tongues, as indicated at l2a.

Fig. 4 is a photomicrograph at the same magniflcation of a ternary alloy containing 0.06% copper, 0.06% tin, and the balance lead, the section being taken in one of the weld regions and repared in the same way as that of Fig. 1. It is o be notedthat there are no black regions of copper oxide in Fig. 3, nor is there a film of copper oxide to make the surface indistinct as in Fig. 1; but, on the contrary, the grain structure is distinct, as in Fig. 3 where the specimen was swabbed, though the Fig. 4 specimen was not swabbed. The weld line is faintly indicated at l I. Grain formation across the weld line is even indicated. When such specimens are swabbed, the weld lines are still more faint.

Fig. 5 is a photomicrograph at the same magnification and of the same ternary alloy as in Fig. 4, but taken in the tongue region and the section prepared in the same way as that of Fig. 2. It was only by careful etching and search that the section was located, even when inspecting the dimensionally charted areas where tongues were u ually found. The tongue 15 is shown only by a very slight shadow or darkening, and the boundaries of the tongue show no distinction whatever in grain structure from the other areas.

Fig. 6 is a photomicrograph at the same magnification and of the same specimen as that shown in Fig. 5 but etched and swabbed like the binary specimen of Fig. 3 to bring out the grain structurein the tongue region for comparison with the same region in the binary alloy sheath shown in Fig. 3. The view would appear substantially the same if it had not been swabbed, because of the absence of copper oxide. It is to be noted that the grains are of uniform size throughout and that there is no concentration of small grains, as in Fig. 3.

When specimens of the binary alloy, such as that shown in Figs. 1, 2 and 3, and that of test specimen No. 1 below, were left for several days in old etching solution (essentially lead acetateacetic acid-alcohol butcontaining a very small amount of copper in solution), they showed a very thick deposit rich in copper (appearing after treatment as copper oxide) over'the entire face, and showed wide black markings of copper oxide at the tongues and welds. The ternary allo s, such as that shown in Figs. 4, 5 and 6, and t e test specimen Nos. 2, 3 and 4 below, when similarly treated showed no such surface deposit and only a very slight discoloration.

Except for very slight markings at the welds, as seen in Fig. 4, and the shadings which can with care be produced at the tongues, as seen in Fig. 5, the ternary alloys acquire the same col-or as commercially pure lead during the etching process. When swabbed, these slight markings disappear and grains of uniform size appear over the entire surface, even across the weld line, as seen in Fig. 6.

In operating an extrusion press to form cable sheaths of the ternary alloy, the desired amount of tin may be added in the melting pot to the molten binary lead-copper alloy; or, if preferred, the ternary lead-copper-tin alloy may be previously formed and supplied to the melting pot as a ternary alloy.

Reference has been made hereinabove to extensive series of tests in which cable sheaths of various types were subjected to internal hydrostatic pressure for various periods of time. In one series, the tests were limited to a predetermined hydrostatic pressure or to a predetermined small amount of expansion as determined by other purposes of the test. In another series, the tests were carried to rupture of the sheath, the time to rupture depending upon the amount of pressure and varying from a few minutes to many months. In another long term group, ex-

tending over a period running up to a few years,

.tion as those from which the accompanying attenuated in the final stages.

'tent. The tensile tests show that the tensile l ance of sheaths formed of the ternary alloy as a homogeneous metal structures, whereas blunt than 7 days, the elongation was less, decreasing the creep characteristics of the alloys were deat which the binary alloy sheaths failed, the itermined by measurements upon strips. ternary alloy sheaths showed the same range of In addition, measurements were made of elongation. The eventual elongation of the fatigue strength and also tensile tests were made ternary alloy sheaths was greater because they on strips out from extruded tubes composed of 5 took longer to fail and the elongation increased binary and ternary alloys of the same composirapidly as the sheaths became progressively more photomicrographs were made, as 'well as from Long term tests were made upon strips cut some other ternary alloys of difierent tin confrom tubing to determine relative cre resiststrength of the ternary alloy was definitely in compared with sheaths formed of the binary althe same range as that of the binary alloy, and loy. For a broad basis of comparison, strips of in one set of tests it proved somewhat superior, common lead were also included in the tests. In

as shown by the following data: these tests constant tension was applied to each specimen and the rate of elongation over various An N C Lead Tensil periods was measured. The results showed that W o W m strength the ternary alloy had a creep rate in the same range as that of the binary alloyactually some- 3- what lower than that of the binary alloy. Otherazso wise expressed, the creep resistance of the gig ternary alloy is as good or better than that of the binary alloy, both being in a range far above that of common lead. The test data, showing gggg ih g g ii gg ggf ga ggfg the creep rate in percent increase in length per alloys was somewhat less than for the samples 25 year for different applied tensile stresses, are as of the above tabulation, but a slight diflerence follows in favor of the ternary alloy was still indicated.

In the first mentioned series of hydraulic presstress in lbw, sure tests-those not intended to be carried to P- failure-it has been noted that sheaths formed l of the binary alloy ruptured with very small 200 elongation occurring in these tests. It is also OREEP RATE IN PERCENT PER YEAR INCREASE noted that sheaths formed of common lead stretched the required amount under the same 35 (J I d conditions but did not break. simii' ar tests were 5 also applied to sheath formed of the ternary al- Te r ay v v iti .c?% 53.,26i%s.3131213112122 I? .8 3

lay and reached the full required amount of t f i1 e. I is elongation and ma thls W1 bout a t On fatigue test with the rotating beam method to be noted that the sheath temperature during these tests was considerably higher than the extruded F P the maxlmum stress below temperature of the lead pipe in the tests in the failure at 20 million cycles was about 700 p. s. 1. following mentioned series which were intenfor eithe? alloy and b u 375 g for tionany carried to faimra Qther data have Corrosion tests of critical sections of the b nary shown that where bursting tests are carried on and terlary alloys revealed conslderable l f at high temperature, less elongation occurs bein thebinary alloy sheath and much less pitting fore failure on sheath containing lines of weakin the ternary alloy sheathness, as in the case of {the binary alloy. Thus, them? is Pmposed as t10 the i l 00nthese binary alloy sheaths, tested at the high the 911? nor the al sicatemperature, failed with much less elongation 5o hs phenomfena 0f mutuajl 5011110111173, F than in the long time tests made at lower tembmty, melting Pomt, and the t0 explam the pemtura reasons for the improvement produced by the In the series of tests with hydraulic pressure inclusion of the th rd metal. It may be regarded i which the tests were purposely carried on melYely modlfymg nt which alters the to failure, it was found that sheath formed of gram me and mlcrostructure m enera (flow the binary alloy be haved entirely differently on lines alfld mngues) and an s the distribution the short time and on the long time tests. For the msolubl? Phase p r)- It is sufficient the test of less than 7 days duration, an elongaljhat pmvqment is in fact produced tion of approximately 20% was obtained and and 110W is p h the breaks were wedge-shaped or gradual, that While 1t 15 belifived h t those skilled in the is, attenuated or drawn out. Wedge-type rupf rfadny recogmze the terms tongues, flowtures are recognized as being characteristic of 111168 d welds as applied to cable sheaths, it may be explained for the benefit of those less For familiar with the art that tongues and flow lines represent boundary surfaces, generally between successive charges, of metal in the press; and welds may represent the same thing or may represent the reuniting surfaces or seams beyond the structures which support the core piece in the press. Tongues and flow lines may be regarded as a part of the charge-weld junctio ruptures indicate non-homogeneous zones. tests at lower pressures which extended for more as the length of the test increased and the failures were radial or abrupt, that is, blunt or almost perpendicular to the wall. 0n the other hand, all of the ruptures in the ternary alloy sheaths were wedge-shaped. Also, the elonga tion on the ternary alloy was as great on th produced between successive charges of meta long time as on the short time test and always as distorted and modified during extrusion. Wit in the same range as the elongation on the short a continuous extrusion press, such as is used time test w th t b y 1 P to the Point ertain special cases, the charge welds will no be present, but the longitudinal seams or weld lines will always be present.

It will thus be seen that the invention provides a ternary alloy which produces a cable sheath having creep strength and fatigue resistance equal to or greater than that of a binary leadcopper alloy but which at the same time has an improved structure free from localized weakness.

When lead is referred to herein, it will be understood that lead of commercial purity is intended. This may contain small amounts of certain other metals. Some of these impurities may be present in the same range as the copper and tin, but since they have no material eflect upon the character of the alloy for present purposes, they need not be considered. The copper itself may be wholly or partly present as an impurity in certain types of lead, and to the extent it is present it need not be added.

It is to be understood that the invention may have various embodiments within the scope of the subjoined claims.

I claim as my invention:

1. An extruded. cable sheath formed of a lead base alloy containing copper in amounts sufiicient to improve resistance to creep and fatigue but not sufllcient to prevent extrusion, characterized by the inclusion of tin in amounts ranging from equal to that of the copper up to' less than .5% of the alloy for suppressing aggregation of copper at the tongues and flow lines without impairment of the creep strength andfatigue resistance of the alloy and the balance lead with 3. An extruded cable sheath formed of a lead base alloy, comprising about 0.06% copper, between about 0.06% and 0.12% tin', and the bal-. ance approximately all lead.

4. An extruded cable sheath formed of a lead base alloy in which copper is included in amounts suflicient to improve resistance to creep and fatigue, characterized by the inclusion of tin in amounts approximately equal to the amounts of copper for suppressing aggregation of copper at the tongues and flow lines without impairment of the creep strength and fatigue resistance of the alloy.

5. An extruded cable sheath formed of an alloy composed of lead and approximately 0.06% copper and tin within a range from about 0.03 to lessthan 0.5%, characterized by homogeneous uniform grain structure and absence of copper concentration at the tongues, flow lines and welds and having mechanical properties, such as tensile strength and resistance to creep and fatigue in the same range as those of the same alloy without tin.

6. An agoy suitable for forming extruded cable sheaths nd the like, comprising copper in amounts between 0.03% and 0.08%, tin in amounts between 0.03% and less than 0.5%, and the balance all lead with usual commercial impurities.

7. An alloy suitable for forming extruded cable sheaths and the like, comprising copper about 0.06%, tin between about 0.06% and 0.12%, and the balance approximately all lead.

8. An alloy suitable for forming extruded cable sheaths and the like, comprising copper about 0.06%, tin about 0.06%, and the balance principally lead.

GABRIEL JOSEPH D'EUSTACHIO. 

